Preparation of acrylic polymer sol for coating

ABSTRACT

Disclosed are acrylic polymer beads and an acrylic sol composition containing the acrylic polymer beads that are used for automobile underbody floor, wheel housing, fuel tank, body panel junction and hood, door, or the like for the purpose of water tightness, vibration isolation, and anticorrosion. More specifically, the acrylic polymer beads having a core/shell structure, which are prepared by using a part of the monomer constituting a core layer to form seeds by a seed polymerization, polymerizing the rest of the monomer to form a core layer and then foaming a shell layer containing an appropriate amount of a crosslink agent, have a narrow particle size distribution and thereby provide, when used in addition to a plasticizer and a filler in the preparation of an acrylic sol composition for automobile, high storage stability of the acrylic sol and excellent properties of the coating formed by gelation of the acrylic sol.

TECHNICAL FIELD

The present invention relates to acrylic polymer beads having acore/shell structure and a uniform particle size distribution, apreparation method thereof, and an acrylic sol composition containingthe acrylic polymer beads. More specifically, the present inventionrelates to a preparation method for acrylic polymer beads that involvespreparing a core/shell type acrylic polymer emulsion having a uniformparticle size with a narrow particle diameter distribution in the rangeof 0.2 to 0.5 μm by an emulsion polymerization method based on seedpolymerization, and spray-drying the prepared acrylic polymer emulsionto form acrylic polymer beads having a particle diameter of 10 to 100μm, and an acrylic sol composition for automobile prepared by mixing theacrylic polymer beads with a plasticizer, a filler, and so forth toprovide with high storage stability and excellent properties of acoating formed by gelation of the acrylic sol.

BACKGROUND ART

The one of the five general-purpose resins, polyvinylchloride (PVC) isused for various applications, such as plastics, films, adhesives, etc.and, primarily for plastic sols. The most popular plastic sol for theindustrial use purpose is the PVC sol that is prepared by dispersion ofPVC powder and fillers in a plasticizer. The PVC sol contains, accordingto its use purpose, a pigment, a thermal stabilizer, a foaming agent, adiluent, and so forth.

The plastic sol is widely used in various applications, includingautomobile, carpet, wallpaper, coating, or the like. In particular, thePVC sol is generally applied to automobile underbody floor, wheelhousing, or fuel tank for the purpose of water tightness, vibrationisolation, and anticorrosion, and automobile body panel junction andhood, door, or the like for the purpose of water tightness andanticorrosion. The PVC sol, however, gives off a hydrogen chloride gasfrom its principal component, PVC during incineration to cause damage onthe incinerator and generation of dioxin as well as acid rain anddestruction of the ozone layer. Due to these problems, the restrictionon the use of the PVC sol has been consolidated with many attempts madeon the substitute of the PVC sol.

Accordingly, Japanese Patent Laid-open Nos. H07-102147, 08-3411 and08-73601 disclose a method for preparing an acrylic polymer and anacrylic sol containing the acrylic polymer. According to the method, theacrylic polymers for sol have a double-layer or multi-layer core/shellstructure that the core layer is comprised of a polymer highlycompatible with a plasticizer, the shell layer being comprised of apolymer poor in compatibility with the plasticizer. The acrylic polymerparticle of the core/shell structure gets storage stability from theshell layer retarding gelation caused by the plasticizer at the storagetemperature, and forms a coating from the polymer of the core layerhighly compatible with the plasticizer at the gelation temperature.

But the acrylic polymer beads as disclosed in those documents have awide particle size distribution in the range of 0.1 to 100 μm and arenot suitable to an acrylic sol for automobile requiring high storagestability.

More specifically, when the acrylic polymer obtained after spry dryingcontains beads having a particle diameter of less than 10 μm, theparticles are readily plasticized at the room temperature after thepreparation of the acrylic sol to rapidly increase the viscosity of thesol with an elapse of time. The reason why these spray-dried beads havea wide particle size distribution is because the primary particles inthe polymerized emulsion state and hence the secondary particles formedafter the spray drying have a wide particle size distribution. Moreover,the high water absorption capacity characteristic to the acrylic polymercauses bubbles in the coating formed by gelation and leads to seriousproblems when coated on the mobile underbody floor, or wheel housing.

To summarize the problems with the prior art, the acrylic polymer beadsaccording to the conventional method for preparing acrylic polymer beadshaving a core/shell structure have a wide particle diameter distributionand contain particles having a particle diameter of less than 10 μm,thereby hardly providing storage stability of the sol. In addition, thehigh water absorption capacity of the acrylic polymer particles causesbubbles in the coating formed by gelation of the acrylic sol todeteriorate the properties of the coating.

In an attempt to solve the problems related to the poor storagestability of the acrylic sol and the deteriorated properties of thecoating formed by gelation in the preparation of acrylic polymer beadshaving a core/shell structure, the inventors of the present inventionhave figured out that a core/shell type acrylic polymer emulsion havinga narrow particle diameter distribution of 0.2 to 0.5 μm can be preparedby using a part of the monomer constituting a core layer to form seedsby a seed polymerization, polymerizing the rest of the monomer to form acore layer and then forming a shell layer containing an appropriateamount of a crosslink agent to form acrylic polymer beads having acore/shell structure.

The inventors of the present invention have also figured out thatacrylic polymer beads having a particle diameter of 10 to 100 μm can beprepared by spray-drying the core/shell type acrylic polymer emulsionand used for the preparation of an acrylic sol having a high storagestability and excellent properties of the coating formed by gelation.

It is therefore an object of the present invention to provide acrylicpolymer beads having a narrow particle size distribution.

It is another object of the present invention to provide a method forpreparing acrylic polymer beads having a core/shell structure and anarrow particle size distribution by seed polymerization.

To achieve the objects of the present invention, there is providedacrylic polymer beads for automobile having an average particle diameterof 0.2 to 0.5 μm, a standard deviation of particle diameter of 1 to 20%with respect to the average particle diameter as measured with aSubmicron Particle Sizer in an emulsion obtained by emulsionpolymerization, and the final average particle diameter of 10 to 100 μm.

In one aspect of the present invention, there is provided a method forpreparing acrylic polymer beads for automobile that uses an emulsionpolymerization and involves preparing an emulsion containing acrylicpolymer beads having a core/shell structure, and spray-drying theemulsion to form acrylic polymer beads. The method includes: (a) addingan ion-exchange water, 5 to 60 wt % of a monomer constituting a corelayer, and an emulsifier, heating the resultant mixture, adding anaqueous initiator, and performing polymerization for 1 to 4 hours toform seeds; (b) adding dropwise the rest of the monomer constituting thecore layer, and further performing polymerization for 1 to 6 hours toform a core layer; (c) adding a monomer constituting a shell layer, andfurther performing the polymerization for 2 to 8 hours to form anemulsion containing acrylic polymer beads having a core/shell structure;and (d) spray-drying the emulsion containing the acrylic polymer beadsto prepare the acrylic polymer beads.

In another aspect of the present invention, there is provided an acrylicsol composition for automobile that includes 100 parts by weight of theacrylic polymer beads having a core/shell structure as obtained by theabove-described method; 50 to 150 parts by weight of a plasticizer; and50 to 150 parts by weight of a filler.

DISCLOSURE OF INVENTION

The present invention involves preparing acrylic polymer beads byemulsion polymerization to have a core/shell structure. In thepolymerization of the core layer, an ion-exchange water, a part of themonomer constituting the core layer, and an emulsifier are mixed, heatedto 60 to 90° C., and treated with an aqueous initiator for 1 to 4polymerization to form seeds. The rest of the monomer for the core layerand the emulsifier are then further added to complete the core layer.Subsequently, a monomer constituting the shell layer is polymerized toobtain an emulsion containing acrylic polymer beads having an averageparticle diameter of 0.2 to 0.5 μm with a standard deviation of 1 to 12%with respect to the average particle diameter. The emulsion isspray-dried to form beads having an average particle diameter of 10 to100 μm. But, the present invention is not specifically limited to thiscore/shell double layer structure.

The acrylic polymer beads obtained by spray-drying the polymerizedemulsion in the present invention have a narrow particle diameterdistribution of 10 to 100 μm. If the beads have a particle diameter ofless than 10 μm, then they are susceptible to gelation by theplasticizer during storage, thereby deteriorating the storage stability.This is a vulnerable point especially for the acrylic sol compositionfor automobile or the like that requires high storage stability.Otherwise, if the beads have a particle diameter exceeding 100 μm, thenthe coating formed by gelation of the beads is non-uniform with theoutflow of the plasticizer. It is therefore important to control theparticle diameter of the beads obtained by spray drying to have a narrowdistribution of 10 to 100 μm. For this purpose, the particles of thepolymerized emulsion are controlled to have an average particle diameterof 0.2 to 0.5 μm with a standard deviation of 1 to 12% with respect tothe average particle diameter.

More specifically, the method for preparing acrylic polymer beads havinga core/shell structure according to the present invention includes thefirst step of adding an ion-exchange water having a resistance ofgreater than 1 mΩ, 5 to 60 wt. % of a monomer constituting the corelayer with an appropriate amount of a crosslink agent, and an emulsifierto a reactor, heating the reactor to an internal temperature of 60 to90° C., and adding an aqueous initiator for 1 to 4 polymerization toform seeds.

The second step of the method involves adding the rest of the monomerconstituting the core layer in an amount of 40 to 95 wt. %, and theemulsifier to the reactor for polymerization to form the core layer.

The third step involves adding a monomer constituting the shell layerwith an appropriate amount of the crosslink agent while maintaining theconstant internal temperature of the reactor, polymerizing the monomer,and further adding an initiator to complete the polymerization andobtain an emulsion containing acrylic polymer beads having a core/shellstructure and an average particle diameter of 0.2 to 0.5 μm with astandard deviation of 1 to 12% with respect to the average particlediameter.

The final step involves spray-drying the polymerized emulsion to preparebeads having an average particle diameter of 10 to 100 μm.

Preferably, the weight ratio (wt %/wt %) of core to shell is 30:70 to75:25.

In the preparation of the acrylic polymer beads having a core/shellstructure, the specific examples of the monomer used for the core layermay include n-butylacrylate, isobutylacrylate, sec-butylacrylate,tert-butylacrylate, butylacrylate, ethylacrylate, styrene,methylmethacrylate, benzylacrylate, or butylacrylate. These monomers canbe used alone or in combination of at least two.

The specific examples of the monomer used for the shell layer mayinclude methylmethacrylate, acrylic acid, methacrylic acid,acrylonitrile, or benzylmethacrylate. These monomers can be used aloneor in combination of at least two.

In the preferred embodiment of the present invention, a crosslink agentcan be further used in addition to the monomers in forming the core andshell layers. The addition of the crosslink agent forms the netstructure of polymer chains and prevents the penetration of theplasticizer to enhance the storage stability of the acrylic sol.

The specific examples of the crosslink agent as used herein may include1,2-ethanedioldi(meta)acrylate, 1,3-propanedioldi(meta)acrylate, 1,4butanedioldi(meta)acrylate, 1,5-hexanedioldi(meta)acrylate,divinylbenzene, ethyleneglycoldi(meta)acrylate,propyleneglycoldi(meta)acrylate, butyleneglycoldi(meta)acrylate,triethyleneglycoldi(meta)acrylate, polyethyleneglycoldi(meta)acrylate,polypropyleneglycoldi(meta)acrylate, polybutyleneglycoldi(meta)acrylate,and allyl(meta)acrylate. These crosslink agents can be used alone or incombination of at least two.

The added amount of the crosslink agent for the core layer is preferably0.1 to 3 parts by weight based on 100 parts of the monomer for the corelayer. If the added amount of the crosslink agent exceeds 3 parts byweight based on 100 parts by weight of the monomer for the core layer,then the coating that must have such a smoothness as rubber becomeshard.

The added amount of the crosslink agent for the shell layer ispreferably 0.1 to 5 parts by weight based on 100 parts of the monomerfor the shell layer. If the added amount of the crosslink agent exceeds5 parts by weight based on 100 parts by weight of the monomer for theshell layer, then the final coating is hardened.

The specific examples of the emulsifier as used herein forpolymerization of the acrylic polymer beads having a core/shellstructure according to the present invention may include anionicemulsifiers, including sodium, ammonium or potassium salts of C₄-C₃₀alkylsulfate (e.g., sodium dodecylsulfate, sodium dioctylsulfosuccinate,sodium dodecylbenzenesulfate, etc.), or reactive emulsifiers oramphoteric emulsifiers of the same system. The content of the emulsifieris preferably 0.1 to 4.0 part by weight based on 100 parts by weight ofthe monomer for each layer.

The ion-exchange water used for polymerization of the acrylic polymerbeads having a core/shell structure according to the present inventionis a purified water having a resistance of more than 5 MΩ in thenitrogen atmosphere as generated from an ion exchanger. The used amountof the ion-exchange water is preferably 80 to 800 parts by weight basedon the total weight of the monomers.

The acrylic polymer beads having a core/shell structure are used toprepare an acrylic sol composition for automobile. More specifically,the acrylic sol composition for automobile may include 100 parts byweight of the acrylic polymer beads, 50 to 150 parts by weight of aplasticizer; and 50 to 150 parts by weight of a filler, and additionallyan adhesive agent or a water absorber.

The specific examples of the plasticizer used for the acrylic solcomposition of the present invention may include phthalate plasticizers(e.g., dibutylphthalate, dioctylphthalate, diisononylphthalate,diisodecylphthalate, butylbenzylphthalate, etc.); phosphate plasticizers(e.g., tricresylphosphate, tri-2-ethylhexylphosphate,cresyldiphenylphosphate, triarylphosphate, etc.); aliphatic plasticizers(e.g., di-2-ethylhexyladiphate, diisodecyladiphate, etc.); or C₅-C₂₀₀lower paraffins or olefins. These plasticizers can be used alone or incombination of at least two.

The content of the plasticizer is preferably 50 to 150 parts by weightbased on 100 parts by weight of the acrylic polymer beads. If thecontent of the plasticizer is less than 50 parts by weight, then the solcomposition cannot be applied by spray coating or the like because ofits extremely high viscosity, and the coating formed by gelation of thesol composition has a low impact strength. Otherwise, if the content ofthe plasticizer exceeds 150 parts by weight, then the sol compositionhas an extremely low viscosity and runs down before the formation of acoating by gelation, and the plasticizer flows out after gelation.

The specific examples of the filler for the acrylic sol composition mayinclude calcium carbonate, talc, clay, silica, mica, kaolin, titaniumdioxide, carbon black, dye, pigment, aluminum hydroxide, bentonite, oraluminum oxide. These fillers can be used alone or in combination of atleast two. The content of the filler is preferably 50 to 150 parts byweight based on 100 parts by weight of the acrylic polymer beads. Thecontent of the filler less than 50 parts by weight deteriorates theproperty-compensating effect of the filler, but the content of thefiller exceeding 150 parts by weight leads to an extremely highviscosity and deteriorates the properties of the coating formed bygelation.

When the acrylic sol composition of the present invention is used as acoating on the automobile underbody and applied to the bottom of anautomobile, the adhesive agent is used for the adhesion to steel plates.Namely, the addition of the adhesive agent is necessary for the adhesivestrength while the automobile is running, in order to maintain the watertightness, vibration isolation, and anticorrosion functions of theacrylic sol applied on the automobile bottom body.

The specific examples of the adhesive agent may include at least oneselected from bisphenol-A epoxy, tetrabromobisphenol-A epoxy,urethane-modified epoxy, rubber-modified epoxy, trifunctional epoxy,tetrafunctional epoxy, polyfunctional bisphenol-A epoxy, phenol novolakepoxy, cresol novolak epoxy, and bisphenol-A novolak epoxy. The contentof the adhesive agent is preferably less than 10 parts by weight basedon 100 parts by weight of the acrylic polymer beads. The content of theadhesive agent exceeding 10 parts by weight deteriorates the storagestability of the sol.

The acrylic sol composition for automobile according to the presentinvention further includes an organic or inorganic water absorber,because the acrylic polymer beads may absorb a large amount of waterduring storage and the water may cause bubbles in the final coating ofthe acrylic sol prepared from the water-containing acrylic polymerparticles.

The specific examples of the water absorber may include at least oneselected from methyltrimethoxysilane, calcium oxide, calcium chloride,silica gel, or calcium hydroxide. The content of the water absorber ispreferably less than 10 parts by weight based on 100 parts by weight ofthe acrylic polymer bead. The content of the water absorber exceeding 10parts by weight may lead to a deterioration of the properties of thecoating formed by gelation.

In the preparation method of the acryl sol of the present invention, aplasticizer is added to a kneader or mixer, and the acrylic polymerbeads, a filler, or, if necessary, an adhesive agent and a waterabsorber are uniformly dispersed to form the acryl sol of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail by way ofthe following examples, which are not intended to limit the scope of thepresent invention.

EXAMPLE 1

In the first step, 600 g of an ion-exchange water was added to a 3l-flask and heated to an internal temperature of 70° C. in the nitrogenatmosphere. A mixed solution containing 200 g of butylmethacrylate as amonomer to be polymerized into the core layer and 2 g of sodiumdioctylpersulfosuccinate was prepared. Only 30 wt. % of the mixedsolution was added to a reactor and stirred at 200 rpm for 15 minutes.Subsequently, the solution was treated with 15 ml of a potassiumpersulfate solution and stirred for 60 minutes for polymerization toform seeds.

In the second step, after the completion of the polymerization, the restof the mixed solution was added dropwise to the reactor over 30 minutesand further polymerized for 4 hours to form a core layer.

After adding 7 ml of the potassium persulfate solution and stirring for30 minutes, in the third step, 10 g of a mixed solution containing 180 gof methylmethacrylate, 20 g of methacrylic acid and 2 g of sodiumdioctylpersulfosuccinate was added dropwise to the reactor over 40minutes, treated with 15 ml of the potassium persulfate solution, andpolymerized for 4 hours. Then, the resultant solution was treated withmore 7 ml of the potassium persulfate solution and further polymerizedfor one hour to complete the polymerization.

The acrylic polymer beads contained in the emulsion thus obtained wereanalyzed in regard to particle diameter and particle diameterdistribution with a Submicron Particle Sizer. In addition, the beads inthe emulsion state were dried with a spray drier having an inlettemperature of 220° C. and an outlet temperature of 88° C. The size ofthe dried acrylic polymer beads was then measured with an opticalmicroscope equipped with an image analyzer.

Subsequently, 100 parts by weight of the dried acrylic polymer beads, 80parts by weight of calcium carbonate as a filler, and 10 parts by weightof an epoxy-based adhesive agent (R-1636-2, supplied by Kukdo ChemicalCo., Ltd.) were dispersed in 135 parts by weight of dioctylphthalateused as a plasticizer to form an acrylic sol.

The sol thus obtained was kept in a thermohydrostat (40° C., 95%) for 14hours and measured in regard to viscosity with a Brookfield ViscometerNo. 7 Spindle at 20° C., and 20 rpm.

The sol was applied to a thickness of 2 mm by airless spray andsubjected to gelation at 150° C. for 40 minutes to analyze the coatingcondition.

EXAMPLE 2

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 1,excepting that 10 wt. % of the monomer for the core layer waspolymerized to form seeds in the first step and that 90 wt. % of themonomer for the core layer was used to form the core layer in the secondstep. The composition of the acrylic sol was the same as presented inExample 1.

EXAMPLE 3

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 1,excepting that 100 parts by weight of the dried acrylic polymer beads,80 parts by weight of calcium carbonate as a filler, 10 parts by weightof an epoxy-based adhesive agent, and 7 parts by weight of calcium oxideas a water absorber were dispersed in 135 parts by weight ofdioctylphthalate used as a plasticizer to prepare an acrylic sol.

COMPARATIVE EXAMPLE 1

600 g of an ion-exchange water was added to a 3 l-flask and heated to aninternal temperature of 70° C. in the nitrogen atmosphere. A mixedsolution containing 200 g of butylmethacrylate as a monomer to bepolymerized into the core layer and 2 g of sodiumdioctylpersulfosuccinate was added to the reactor and stirred at 200 rpmfor 15 minutes. Subsequently, the solution was treated with 20 ml of apotassium persulfate solution and stirred for 4 hours for polymerizationto form a core layer.

After adding 7 ml of the potassium persulfate solution and stirring for30 minutes, 10 g of a mixed solution containing 180 g ofmethylmethacrylate, 20 g of methacrylic acid and 2 g of sodiumdioctylpersulfosuccinate was added dropwise to the reactor over 40minutes, treated with 15 ml of the potassium persulfate solution, andpolymerized for 4 hours. Then, the resultant solution was treated withmore 7 ml of the potassium persulfate solution and further polymerizedfor one hour to complete the polymerization. The following procedureswere performed in the same manner as described in Example 1 to dry anemulsion containing the acrylic polymer beads.

Subsequently, 100 parts by weight of the dried acrylic polymer beads, 80parts by weight of calcium carbonate as a filler, and 10 parts by weightof an epoxy-based adhesive agent were dispersed in 135 parts by weightof dioctylphthalate used as a plasticizer to form an acrylic sol.

COMPARATIVE EXAMPLE 2

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 1,excepting that 3 wt. % of the monomer for the core layer was polymerizedto form seeds in the first step and that 97 wt. % of the monomer for thecore layer was used to form the core layer in the second step. Thedrying procedure after the completion of the polymerization and thecomposition of the acrylic sol were the same as described in Example 1.

The properties of the acrylic polymer beads and the acrylic solsprepared from the acrylic polymer beads according to Examples 1, 2 and3, and Comparative Examples 1 and 2 are presented in Table 1. TABLE 1Average Particle Particle Size (nm) Diameter (μm) (Standard (StandardAcrylic Sol Deviation, nm) of Deviation, nm) Viscosity (cps) AdhesiveAcrylic Polymer After Spray After 14 Strength Coating Bead in EmulsionDrying Initial days (kg/cm²) Condition A 1 280 (15) 40 (5) 48,300 59,8008.2 ⊚ (Bubble) 2 420 (25)  83 (11) 60,400 72,400 7.7 ◯ (Bubble) 3 280(15) 40 (5) 51,800 61,900 7.3 ⊚ B 1 185 (32) 19 (7) 32,400 78,800 8.2 ◯(Bubble) 2 480 (70) 120 (38) 74,600 116,400 6.8 Δ (Bubble)Note)A: ExampleB: Comparative Example

EXAMPLE 4

In the first step, 600 g of an ion-exchange water was added to a 3l-flask and heated to an internal temperature of 70° C. in the nitrogenatmosphere. A mixed solution containing 200 g of butylmethacrylate as amonomer to be polymerized into the core layer, 2 g ofallyl(meta)acrylate, and 2 g of sodium dioctylpersulfosuccinate wasprepared. Only 30 wt. % of the mixed solution was added to a reactor andstirred at 200 rpm for 15 minutes. Subsequently, the solution wastreated with 15 ml of a potassium persulfate solution and stirred for 60minutes for polymerization to form seeds.

In the second step, after the completion of the polymerization, the restof the mixed solution was added dropwise to the reactor over 30 minutesand further polymerized for 4 hours to form a core layer.

After adding 7 ml of the potassium persulfate solution and stirring for30 minutes, in the third step, 10 g of a mixed solution containing 180 gof methylmethacrylate, 20 g of methacrylic acid, 5 g ofallyl(meta)acrylate, and 2 g of sodium dioctylpersulfosuccinate wasadded dropwise to the reactor over 40 minutes, treated with 15 ml of thepotassium persulfate solution, and polymerized for 4 hours. Then, theresultant solution was treated with more 7 ml of the potassiumpersulfate solution and further polymerized for one hour to complete thepolymerization.

The acrylic polymer beads contained in the emulsion thus obtained wereanalyzed in regard to particle diameter and particle diameterdistribution with a submicron particle sizer. In addition, the beads inthe emulsion state were dried with a spray drier having an inlettemperature of 220° C. and an outlet temperature of 88° C. The size ofthe dried acrylic polymer beads was then measured with an opticalmicroscope equipped with an image analyzer.

Subsequently, 100 parts by weight of the dried acrylic polymer beads, 80parts by weight of calcium carbonate as a filler, and 10 parts by weightof an epoxy-based adhesive agent (R-1636-2, supplied by Kukdo ChemicalCo., Ltd.) were dispersed in 135 parts by weight of dioctylphthalateused as a plasticizer to form an acrylic sol.

The sol thus obtained was kept in a thermohydrostat (40° C., 95%) for 14hours and measured in regard to viscosity with a Brookfield ViscometerNo. 7 Spindle at 20° C., and 20 rpm.

The sol was applied to a thickness of 2 mm by airless spray andsubjected to gelation at 150° C. for 40 minutes to analyze the coatingcondition.

EXAMPLE 5

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 4,excepting that 10 wt. % of the monomer for the core layer waspolymerized to form seeds in the first step and that 90 wt. % of themonomer for the core layer was used to form the core layer in the secondstep. The composition of the acrylic sol was the same as presented inExample 4.

EXAMPLE 6

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 4,excepting that 100 parts by weight of the dried acrylic polymer beads,80 parts by weight of calcium carbonate as a filler, 10 parts by weightof an epoxy-based adhesive agent, and 7 parts by weight of calcium oxideas a water absorber were dispersed in 135 parts by weight ofdioctylphthalate used as a plasticizer to prepare an acrylic sol.

COMPARATIVE EXAMPLE 3

600 g of an ion-exchange water was added to a 3 l-flask and heated to aninternal temperature of 70° C. in the nitrogen atmosphere. A mixedsolution containing 200 g of butylmethacrylate as a monomer to bepolymerized into the core layer, 2 g of allyl(meta)acrylate, and 2 g ofsodium dioctylpersulfosuccinate was added to the reactor and stirred at200 rpm for 15 minutes. Subsequently, the solution was treated with 20ml of a potassium persulfate solution and stirred for 4 hours forpolymerization to form a core layer.

After adding 7 ml of the potassium persulfate solution and stirring for30 minutes, 10 g of a mixed solution containing 180 g ofmethylmethacrylate, 20 g of methacrylic acid, 2 g ofallyl(meta)acrylate, and 2 g of sodium dioctylpersulfosuccinate wasadded dropwise to the reactor over 40 minutes, treated with 15 ml of thepotassium persulfate solution, and polymerized for 4 hours. Then, theresultant solution was treated with more 7 ml of the potassiumpersulfate solution and further polymerized for one hour to complete thepolymerization. The following procedures were performed in the samemanner as described in Example 4 to dry an emulsion containing theacrylic polymer beads.

Subsequently, 100 parts by weight of the dried acrylic polymer beads, 80parts by weight of calcium carbonate as a filler, and 10 parts by weightof an epoxy-based adhesive agent were dispersed in 135 parts by weightof dioctylphthalate used as a plasticizer to form an acrylic sol.

COMPARATIVE EXAMPLE 4

The procedures were performed to prepare acrylic polymer beads having acore/shell structure in the same manner as described in Example 4,excepting that 3 wt. % of the monomer for the core layer was polymerizedto form seeds in the first step and that 97 wt. % of the monomer for thecore layer was used to form the core layer in the second step. Thedrying procedure after the completion of the polymerization and thecomposition of the acrylic sol were the same as described in Example 4.

The properties of the acrylic polymer beads and the acrylic solsprepared from the acrylic polymer beads according to Examples 4, 5 and6, and Comparative Examples 3 and 4 are presented in Table 2. TABLE 2Average Particle Particle Size (nm) Diameter (μm) (Standard (StandardAcrylic Sol Deviation, nm) of Deviation, nm) Viscosity (cps) AdhesiveAcrylic Polymer After Spray After 14 Strength Coating Bead in EmulsionDrying Initial days (kg/cm²) Condition A 4 280 (15) 40 (5) 44,300 51,8008.2 ⊚ (Bubble) 5 420 (25)  83 (11) 56,400 64,400 7.7 ◯ (Bubble) 6 280(15) 40 (5) 46,800 53,900 7.3 ⊚ B 3 185 (32) 19 (7) 33,600 68,700 8.2 ◯(Bubble) 4 480 (70) 120 (38) 65,300 97,500 6.8 Δ (Bubble)Note)A: ExampleB: Comparative Example

INDUSTRIAL APPLICABILITY

The acrylic polymer beads having a core/shell structure according to thepresent invention, which are prepared by using a part of the monomerconstituting a core layer to form seeds by a seed polymerization,polymerizing the rest of the monomer to form a core layer and thenforming a shell layer, have a narrow particle size distribution andthereby provide, when used in addition to a plasticizer and a filler inthe preparation of an acrylic sol composition for automobile, highstorage stability of the acrylic sol and excellent properties of thecoating formed by gelation of the acrylic sol. Particularly, theaddition of a crosslink agent can enhance the storage stability of theacrylic sol. Accordingly, the acrylic sol composition thus obtained canbe applied, as a substitute for the PVC sol, to the automobile underbodyfloor, wheel housing, fuel tank, body panel junction and hood, door, orthe like for the purpose of water tightness, vibration isolation, andanticorrosion.

While this invention has been described in connection with theembodiments, it is to be understood to those skilled in the art that theinvention is not limited to the disclosed embodiments, but, on thecontrary, is intended to cover various modifications and equivalentarrangements. Particularly, the number of layers is flexible and thecore/shell structure can have a gradient. Accordingly, the technicalcoverage of the present invention is to be included within the spiritand scope of the appended claims.

1. An acrylic polymer bead for automobile having an average particlediameter of 0.2 to 0.5 μm, a standard deviation of particle diameter of1 to 20% with respect to the average particle diameter as measured witha Submicron Particle Sizer in an emulsion obtained by emulsionpolymerization, and the final average particle diameter of 10 to 100 μm.2. A method for preparing acrylic polymer beads for automobile, whichbeads have an average particle diameter of 0.2 to 0.5 μm and a standarddeviation of particle diameter of 1 to 20% with respect to the averageparticle diameter as measured with a Submicron Particle Sizer in anemulsion obtained by emulsion polymerization, the final average particlediameter after spray drying being 10 to 100 μm, the method comprising:(a) adding an ion-exchange water, 5 to 60 wt. % of a monomerconstituting a core layer, and an emulsifier to a reactor, heating thereactor, adding an aqueous initiator, and performing polymerization toform seeds; (b) adding dropwise the rest of the monomer constituting thecore layer, and further performing polymerization to form a core layer;(c) adding a monomer constituting a shell layer, and further performingpolymerization to form an emulsion containing acrylic polymer beadshaving a core/shell structure; and (d) spray-drying the emulsioncontaining acrylic polymer beads to prepare acrylic polymer beads. 3.The method as claimed in claim 2, wherein a crosslink agent isadditionally used, the crosslink agent being at least one selected fromthe group consisting of 1,2-ethanedioldi(meta)acrylate,1,3-propanedioldi(meta)acrylate, 1,4-butanedioldi(meta)acrylate,1,5-pentanedioldi(meta)acrylate, 1,6-hexanedioldi(meta)acrylate,divinylbenzene, ethyleneglycoldi(meta)acrylate,propyleneglycoldi(meta)acrylate, butyleneglycoldi(meta)acrylate,triethyleneglycoldi(meta)acrylate, polyethyleneglycoldi(meta)acrylate,polypropyleneglycoldi(meta)acrylate, polybutyleneglycoldi(meta)acrylate,and allyl(meta)acrylate.
 4. The method as claimed in claim 2, wherein acrosslink agent is additionally used in an amount of 0.1 to 3 parts byweight based on 100 parts by weight of the monomer constituting the corelayer during formation of the core layer, and 0.1 to 5 parts by weightbased on 100 parts by weight of the monomer constituting the shell layerduring formation of the shell layer.
 5. An acrylic sol composition forautomobile comprising 100 parts by weight of the acrylic polymer beadsaccording to claim 1; 50 to 150 parts by weight of a plasticizer; and 50to 150 parts by weight of a filler.
 6. The acrylic sol composition forautomobile as claimed in claim 5, further comprising at most 10 parts byweight of at least one water absorber selected frommethyltrimethoxysilane, calcium oxide, calcium chloride, silica gel andcalcium hydroxide.
 7. The acrylic sol composition for automobile asclaimed in claim 5, further comprising at most 10 parts by weight of atleast one adhesive agent selected from bisphenol-A epoxy,tetrabromobisphenol-A epoxy, urethane-modified epoxy, rubber-modifiedepoxy, trifunctional epoxy, tetrafunctional epoxy, polyfunctionalbisphenol-A epoxy, phenol novolak epoxy, cresol novolak epoxy andbisphenol-A novolak epoxy.
 8. The acrylic sol composition for automobileas claimed in claim 6, further comprising at most 10 parts by weight ofat least one adhesive agent selected from bisphenol-A epoxy,tetrabromobisphenol-A epoxy, urethane-modified epoxy, rubber-modifiedepoxy, trifunctional epoxy, tetrafunctional epoxy, polyfunctionalbisphenol-A epoxy, phenol novolak epoxy, cresol novolak epoxy andbisphenol-A novolak epoxy.
 9. The acrylic sol composition for automobileas claimed in claim 5, wherein the composition has an initial viscosityof 30,000 to 80,000 cps as measured with a Brookfield Viscometer No. 7Spindle at 20° C. and 20 rpm, and a viscosity increment of less than 30%with respect to the initial viscosity as measured in the same conditionsafter 14 days of storage in a thermohydrostat (40° C., 95%).
 10. Anacrylic sol composition for automobile comprising 100 parts by weight ofthe acrylic polymer beads according to claim 2; 50 to 150 parts byweight of a plasticizer; and 50 to 150 parts by weight of a filler. 11.The acrylic sol composition for automobile as claimed in claim 10,further comprising at most 10 parts by weight of at least one waterabsorber selected from methyltrimethoxysilane, calcium oxide, calciumchloride, silica gel and calcium hydroxide.
 12. The acrylic solcomposition for automobile as claimed in claim 10, further comprising atmost 10 parts by weight of at least one adhesive agent selected frombisphenol-A epoxy, tetrabromobisphenol-A epoxy, urethane-modified epoxy,rubber-modified epoxy, trifunctional epoxy, tetrafunctional epoxy,polyfunctional bisphenol-A epoxy, phenol novolak epoxy, cresol novolakepoxy and bisphenol-A novolak epoxy.
 13. The acrylic sol composition forautomobile as claimed in claim 11, further comprising at most 10 partsby weight of at least one adhesive agent selected from bisphenol-Aepoxy, tetrabromobisphenol-A epoxy, urethane-modified epoxy,rubber-modified epoxy, trifunctional epoxy, tetrafunctional epoxy,polyfunctional bisphenol-A epoxy, phenol novolak epoxy, cresol novolakepoxy and bisphenol-A novolak epoxy.
 14. The acrylic sol composition forautomobile as claimed in claim 10, wherein the composition has aninitial viscosity of 30,000 to 80,000 cps as measured with a BrookfieldViscometer No. 7 Spindle at 20° C. and 20 rpm, and a viscosity incrementof less than 30% with respect to the initial viscosity as measured inthe same conditions after 14 days of storage in a thermohydrostat (40°C., 95%).